Our family each has multiple ecredits that we want to use for new trip. After applying the ecredits to the new trip, each of us still has remaining ecredit balance and was issued a new ecredit.
The leftover ecredit on my account and my wife's account have the same expiration date as the old ecredit with the earlier expiration.
My daughter's leftover ecredit has the same expiration date as the old ecredit with the later expiration date.
I don't know how the system determines which ecredit to apply first. I even asked a Delta rep to rebook the ticket but ended up with the same result.
Is there a way to tell the system to use the ecredits with the earlier expiration dates first? Thanks.

Edit: I noticed that at the booking confirmation page, the website showed the correct expiration date for the ecredit balance, but when I went back into my account to view the ecredit, it shows a different expiration date (earlier date).